This invention relates to clean rooms of the general type in use in manufacturing operations requiring dust-free and/or aseptic environments. In semiconductor plants, for example, the need has increased for superclean manufacturing space to facilitate improved manufacturing techniques such as high integration and microminiaturization. Further, the need for clean room facilities has increased to facilitate improvements in full automation equipment, automatic transfer machines, unmanned production lines, and the like.
Generally a clean room includes an air laminar flow system in which a high efficiency particulate air filter (HEPA) is installed over the entire ceiling surface of the clean room and an air blower system in which the clean rooms may be classified in terms of the number of air-borne particles per cubic foot of air in the room. Thus, Class 100 indicates a high degree of cleanliness; Class 1000 indicates an intermediate degree of cleanliness; and Class 10,000 a lower degree of cleanliness wherein cleanliness is a function of air pressure, velocity, and filtering capacity.
In a prior art Class 100 clean room the entire ceiling may comprise the filtering means. Thus, as shown in FIG. 1, an HEPA filter 1 is mounted across the entire ceiling surface. Air is forced through this filter with uniform speed from a supply chamber 2. The air flows vertically downward into a return chamber 3 from which it is recirculated by means of an air conditioner 4. The system shown in FIG. 1 has several problems:
(i) The intitial installation cost is high because the HEPA filter should be mounted over the entire ceiling surface and a heavy duty air conditioner is needed to achieve complete air flow.
(ii) The operating cost is high because a driven fan is necessary for the air conditioner in order to obtain complete air flow.
(iii) The capacity of the fan must be so great that it becomes a source of vibration.
To solve the foregoing problems, another prior art system has been proposed in which sections needing particular cleanliness are situated in clean areas 5 as shown in FIG. 2.
This system also presents problems:
(i) Fans 6 and duct 7 in the ceiling provide for little flexibility and render maintenance difficult.
(ii) The vibration of the fan is transmitted to the floor.
(iii) The air flow becomes turbulent around the clean area line boundaries.
(iv) The cost and time required for installation are increased because of the need for additional ductwork.